1. Field of the Invention
The present invention pertains to the operation and control of a manufacturing process flow, and, more particularly, to deciding when to begin processing an incomplete batch.
2. Description of the Related Art
Growing technological requirements and the worldwide acceptance of sophisticated electronic devices have created an unprecedented demand for large-scale, complex, integrated circuits. Competition in the semiconductor industry requires that products be designed, manufactured, and marketed in the most efficient manner possible. This requires improvements in fabrication technology to keep pace with the rapid improvements in the electronics industry. Meeting these demands spawns many technological advances in materials and processing equipment and significantly increases the number of integrated circuit designs. These improvements also require effective utilization of computing resources and other highly sophisticated equipment to aid, not only design and fabrication, but also the scheduling, control, and automation of the manufacturing process.
Turning first to fabrication, integrated circuits, or microchips, are manufactured from modern semiconductor devices containing numerous structures or features, typically the size of a few micrometers. The features are placed in localized areas of a semiconducting substrate, and are either conductive, non-conductive, or semi-conductive (i.e., rendered conductive in defined areas with dopants). The fabrication process generally involves processing a number of wafers through a series of fabrication tools. Each fabrication tool performs one or more of four basic operations discussed more fully below. The four basic operations are performed in accordance with an overall process to finally produce the finished semiconductor devices.
Integrated circuits are manufactured from wafers of a semiconducting substrate material. Layers of materials are added, removed, and/or treated during fabrication to create the integrated, electrical circuits that make up the device. The fabrication essentially comprises the following four basic operations:                layering, or adding thin layers of various materials to a wafer from which a semiconductor is produced;        patterning, or removing selected portions of added layers;        doping, or placing specific amounts of dopants in selected portions of the wafer through openings in the added layers; and        heat treating, or heating and cooling the materials to produce desired effects in the processed wafer.Although there are only four basic operations, they can be combined in hundreds of different ways, depending upon the particular fabrication process. See, e.g., Peter Van Zant, Microchip Fabrication A Practical Guide to Semiconductor Processing (3d Ed. 1997 McGraw-Hill Companies, Inc.) (ISBN 0-07-067250-4).        
The wafers are processed through a series of process tools that perform one or more of the operations listed above on any given wafer. Frequently, wafers are grouped into lots and processed as “lots.” Sometimes, lots of wafers are grouped into “batches,” and processed by the batch. The process tools may be referred to in the aggregate as a “process flow.” Not all process tools in a process flow perform operations on wafers. Some process tools measure selected aspects of the process flow's performance, and are sometimes more specifically referred to as metrology tools. Wafers, lots, and batches are moved through the process flow, machine by machine according to a schedule. More particularly, a wafer, lot or batch is transported to a machine, the machine performs its scheduled task, and the wafer, lot or batch is transported to the next machine.
Efficient management of a facility for manufacturing products such as semiconductor chips requires monitoring various aspects of the manufacturing process. For example, it is typically desirable to track the amount of raw materials on hand, the status of work-in-process and the status and availability of machines and tools at every step in the process. One of the most important decisions is selecting which lot should run on each machine at any given time. Additionally, most machines used in the manufacturing process require scheduling of routine preventative maintenance (“PM”) and equipment qualification (“Qual”) procedures, as well as other diagnostic and reconditioning procedures that must be performed on a regular basis, such that the performance of the procedures does not impede the manufacturing process itself.
One approach to this issue implements an automated “Manufacturing Execution System” (“MES”). An automated MES enables a user to view and manipulate, to a limited extent, the status of machines and tools, or “entities,” in a manufacturing environment. In addition, an MES enables the dispatching and tracking of lots or work-in-process through the manufacturing process to enable resources to be managed in the most efficient manner. Specifically, in response to MES prompts, a user inputs requested information regarding work-in-process and entity status. For example, when a user performs a PM on a particular entity, the operator logs the performance of the PM (an “event”) into an MES screen to update the information stored in the MES database with respect to the status of that entity. Alternatively, if an entity is to be taken down for repair or maintenance, the operator will log this information into the MES database, which then prevents use of the entity until it is subsequently logged back up.
Although MES systems are sufficient for tracking lots and machines, such systems suffer several deficiencies, the most obvious of which are their passive nature, lack of advance scheduling, and inability to support highly automated factory operations Current MES systems largely depend on manufacturing personnel for monitoring factory state and initiating activities at the correct time. For example, a lot does not begin processing until a wafer fab technician (“WFT”) issues the appropriate MES command. And, prior to processing, a WFT must issue an MES command to retrieve the lot from the automated material handling system (“AMHS”) with sufficient advance planning that the lot is available at the machine when the machine becomes available. If the WFT does not retrieve the lot soon enough, or neglects to initiate processing at the earliest available time, the machine becomes idle and production is adversely impacted.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.